map | 易学教程

Why does the map.insert() method invoke the copy constructor twice?

阅读更多关于 Why does the map.insert() method invoke the copy constructor twice?

问题 I'm creating the custom class Node in order to implement a binary tree using a map<int,Node> container: the int key of the map is the identifier of a Node object. In the class Node I had to implement a copy constructor. When inserting a Node object on the map, I noticed that the copy constructor of the Node is invoked twice. Why? cout << "node2" << endl; Node node2; node2.set_depth(2); node2.make_it_branch(3,4); cout << "map" << endl; map<int,Node> mapping; cout << "toInsert" << endl; pair

Ajax pass a “Map” object to Spring MVC Controller

阅读更多关于 Ajax pass a “Map” object to Spring MVC Controller

问题 It seems like Spring MVC doesn't know how to map a javascript "map" to a Java map object In the web UI, say, foo.jsp, <script> var myMap = {}; myMap["people"] = ["Alex","Bob","Charles","Dave"]; myMap["fruit"] = ["Apple","Orange"]; $.ajax({ type : "POST", url : "/myURL", data : "myMap=" + myMap, // I tried "myMap="+JSON.stringify(myMap), as well, it doesn't work neither success : function(response) { alert("Success! response = " + response); }, error : function(e) { alert("AJAX error"); } });

override map::compare with lambda function directly

阅读更多关于 override map::compare with lambda function directly

问题 Trying to override map::compare function using lambda, it seems that the following solution works. auto cmp = [](const int&a, const int& b) { return a < b; }; std::map<int, int, decltype(cmp)> myMap(cmp); But, I had to define cmp first and use it later. Can I do this without defining 'cmp'? 回答1: No, you can't use lambda in unevaluated context -- i.e. template parameters as in your example. So you must define it somewhere else (using auto ) and then use decltype ... the other way, as it was

How do you pin point the location of a user with 3 nodes, using Triangulation?

阅读更多关于 How do you pin point the location of a user with 3 nodes, using Triangulation?

问题 I am trying to find a user through their Bluetooth strength (RSSI value). I have 3 Raspberry PIs, each gathering the signal strength of the user. Lets say the nodes returned: node1 = 65 node2 = 70 node3 = 75 How would I find the user through triangulation and pin point them on a map, and output the RSSI value? I have researched Trilateration and Ceva's Theorem but do not know how to implement them. I am unsure on how to locate the nodes in an environment, do I give the main node a location of

How do you pin point the location of a user with 3 nodes, using Triangulation?

阅读更多关于 How do you pin point the location of a user with 3 nodes, using Triangulation?

Convert Latitude and Longitude values to a custom sized grid

阅读更多关于 Convert Latitude and Longitude values to a custom sized grid

问题 I am making a java program that classifies a set of lat/lng coordinates to a specific rectangle of a custom size, so in effect, map the surface of the earth into a custom grid and be able to identify what rectangle/ polygon a point lies in. The way to do this I am looking into is by using a map projection (possibly Mercator). For example, assuming I want to classify a long/lat into 'squares' of 100m x 100m, 44.727549, 10.419704 and 44.727572, 10.420460 would classify to area X and 44.732496,

Modify dict values inplace

阅读更多关于 Modify dict values inplace

问题 I would like to apply a function to values of a dict inplace in the dict (like map in a functional programming setting). Let's say I have this dict : d = { 'a':2, 'b':3 } I want to apply the function divide by 2.0 to all values of the dict, leading to: d = { 'a':1., 'b':1.5 } What is the simplest way to do that? I use Python 3 . Edit: A one-liner would be nice. The divide by 2 is just an example, I need the function to be a parameter. 回答1: You may find multiply is still faster than dividing

【Java基础】集合

阅读更多关于【Java基础】集合

一、Collection接口（超级接口:Iterator）其下有两个子接口，Set和List。 1）Set接口的两个常用子类 TreeSet：有序存放 HashSet：散列存放 2）List接口（允许重复元素）常用子类:LinkedList、ArrayList、Vector。ArrayList是List接口最常用的一个子类。LinkedList完成的是一个链表操作。二、Map接口实现子类：HashMap、HashTable、TreeMap等 TreeMap与TreeSet类似，TreeMap中元素根据key自动排序。三、集合元素为自定义类时，集合的排序问题及输出自定义类作为集合元素时，集合本身不知道如何排序，必须类实现Comparable接口，并覆写compareTo()方法。 public class Person implements Comparable<Person> { private String name; private int age; public Person(String name, int age) { this.age = age; this.name = name; } @Override public int compareTo(Person o) {//按名字顺序排序 return this.name.compareTo(o.name

check current location is in MkPolygons

阅读更多关于 check current location is in MkPolygons

问题 I am working in an IOS 7 project ,it contains a location checking (current location is in given polygons). I am Using the following code to check the condition Created an array of MKPolygons for(MKPolygon *poly in self.polygonArray) { [self checkTheLocationIsInPolygon:currentLocation polygon:poly]; } - (void)checkTheLocationIsInPolygon:(CLLocation*)aLocation polygon:(MKPolygon*)aPolygon { CLLocationCoordinate2D coordinate = {aLocation.coordinate.latitude, aLocation.coordinate.longitude};

check current location is in MkPolygons

阅读更多关于 check current location is in MkPolygons